It has been known that the diffraction efficiency of a diffractive optical element including a sawblade-like diffraction grating (blazed grating) is improved in a manner in which a film is formed on a grating wall surface to form a waveguide.
PTL 1 discloses a diffractive optical element having a waveguide.
PTL 1 also discloses that films are formed on grating wall surfaces, and at this time, films are formed also on grating surfaces to readily obtain the diffractive optical element having the waveguide at a low cost.